The present invention concerns an operating switch for one or more lamps, particularly low-pressure discharge lamps, which will be operated with a high-frequency power. The high-frequency operation of low-pressure discharge lamps has the advantage of a clear increase in the efficiency of the lamp, in addition to avoiding a mains-frequency radiation of the irradiated light with mains operation. Refer to C. H. Sturm and E. Klein "Operating devices and circuits for electrical lamps", 6th Edition, 1992, Siemens AG, particularly pages 121 to 137, as well as to W. Hirschmann "Electronic circuits", 1982, Siemens AG, pages 147 and 148 for an introduction to basic circuit construction of corresponding ballast devices.
A circuit for high-frequency operation is shown in EP 0 253,224 B1, by which the invention is limited. This circuit of the state of the art has a resonance capacitor for lamp ignition connected directly parallel to the lamp proceeding via the named components, as well as a capacitor connected between the central tap of the push-pull frequency generator and the central tap between the diodes of one of the pump branches (the capacitors are denoted there as C6 or C7). FIG. 1 shows the corresponding circuit structure, whereby the above capacitors are denoted there as C6 or CT2. For a further description of this circuit, refer to the description of the invention given below, for which the example of embodiment shown in FIG. 2 is constructed on the circuit shown in FIG. 1.
Electronic ballast devices for lamps driven with high frequency generally show high-frequency feedback to the mains (with mains operation) or another voltage source as well as a high-frequency electromagnetic irradiation. The sensitivity of other electronic devices and the increasingly dense packing of such devices in the direct operating environment of electronic ballast devices for lamps, however, places increasing requirements for electromagnetic compatibility of an electronic ballast device, which is a potential source of high-frequency interference. Refer to C. H. Sturm and E. Klein (op. cit., p. 122 ff).